IOWA CITY, IOWA—An analysis of DNA taken from Native Americans has been used to get to the roots of how people arrived in America. Scientists at the University of Iowa looked at genetic material taken from 41 Native Americans and compared it with older data to probe those people's origins. According to their findings, three separate migration waves are responsible for seeding the Americas with people, beginning 15,000 to 18,000 years ago. Their findings support archaeological evidence that the intial migration was along the west coast, followed a few thousand years later by a Siberian wave that moved through an ice-free corridor in Alaska. A third wave happened just 4,000 years ago and populated Canada, moving eastward instead of south.